Hematite magnetic ordering

Hoffman KA (1975) Cation diffusion processes and self-reversal of thermoremanent magnetization in the ilmenite-hematite solid solution series. Geophys J Royal Astro Soc 41 65-80 Hoffman KA (1992) Self-Reversal of thermoremanent magnetization in the ilmenite-hematite system Order-disorder, synunetry, and spin aligmnent. J Geophys Res 97 10883-10895... 

As shown in the Table 111, the Reaction equation 1 is easily react, even the equilibrium partial pressure 0(CO) is extremely small. Actually, it is a complete reaction irreversible chemical reaction, however, the equilibrium partial pressure 0(CO) of the reaction equation 2 and 3 are large under the condition of the temperature is 650°C-800°C. In order to guarantee the hematite not to over reduction to FeO, the CO concentration should be strictly controlled in the experimental process. The thermodynamic study of the oolitic hematite magnetic roasting indicates that the thermodynamic tendency is pretty dramatic if the hematite is reduced to the magnetite. 

The major fraction in aU samples consists of magnetically ordered iron oxides, mainly magnetite (apart from samples 3.1 and 3.2, where goethite and hematite also... 

Ozaki, M. Suzuki, H. Takahashi, K. Matijevic, E. (1986) Reversible ordered agglomeration of hematite particles due to weak magnetic interactions. J. Colloid Interface Sci. 

Brown, N.E., Navrotsky, A., Nord, G.L., Baneijee, S.K. (1993) Hematite (Fe203)-ilmenite (FeTiOs) solid solutions Determinations of FeTi order from magnetic properties. Am Mineral 78 941-951 Burton, B.P. (1987) Theoretical analysis of cation ordering in binary rhombohedral carbonate systems. Am Mineral 72 329-336... 

Nord, G.L., Lawsort, C.A. (1989) Order-disorder transition-induced twin domains and magnetic properties in ihnenite-hematite. Am Mineral 74 160-176... 

Figure 13. Model of self-reversal in the ilmenite-hematite solid solution (after Hoffman 1992). Boxes represent (001) cation layers (viewed down the c-axis), shaded according to their Fe-occupancy (Fe = dark, Ti = light). Two ordered ferrimagnetic domains are shown (left and right) separated by a twin wall (central) with a canted antiferromagnetic stmeture. (a) The twin wall orders first with its parasitic moment parallel to the external field. The ferrimagnetic domains order perpendicular to external field and antiparallel to each other, (b) The domain moments tilt away from the wall moment at lower temperatnres, creating a large reverse component of magnetization.

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